1. Field of the Invention
The present invention relates to an antenna duplexer which, for example, can handle individually a transmitted signal and a received signal of a portable telephone or the like, and to a mobile communication device.
2. Related Art of the Invention
In recent years, in mobile communication devices, a frequency-division system capable of simultaneously transmission and reception has been used in systems such as CDMA and the like, and it has attracted attention from the standpoint of expansion of the transmission information content of data communications and the like. In order to make such a simultaneous transmission and reception possible, a shared antenna unit that handles individually the transmitted signal and the received signal, has been widely used. Furthermore, regarding the mobile communication devices such as portable telephones and the like, in order to realize miniaturization and high performance, miniaturization of the sharing unit and a low-loss have been given much attention.
Regarding the systems, which are not of simultaneous transmission and reception such as GSM and the like, antenna switches have been widely used. With respect to these switches, however, though miniaturization and low-loss have been realized due to a constitution having a semiconductor IC and a pin diode, they are not adaptable to simultaneous transmission and reception.
Hereinafter, one example of a conventional sharing unit will be described with reference to the drawings. Note that FIG. 10 shows an equivalent circuit of a conventional sharing unit and the like.
In FIG. 10, the sharing unit 1001 is constituted by a transmitting filter 1002 which is a low-pass filter (LPF) arranged at the transmitting side, a receiving filter 1003 which is a band-pass filter (BPF) arranged at the receiving side, an antenna terminal (ANT) 1004, a transmitting terminal (Tx) 1005 and a receiving terminal (Rx) 1006. The transmitting filter 1002, the receiving filter 1003 and the antenna terminal 1004 are connected via a common terminal 1007. The transmitted signal inputted from the transmitting terminal 1005 is transmitted to the antenna terminal 1004 via the transmitting filter 1002.
At this time, since the impedance of the transmitted frequency band from the common terminal 1007 toward the band-pass filter 1003 of the receiving side, is ideally adjusted to be in an open state, the transmitted signal is not transmitted to the receiving terminal 1006. The received signal inputted from the antenna terminal 1004 is transmitted to the receiving terminal 1006 via the band-pass filter 1003 of the receiving side. At this time, since the impedance of the reception frequency band from the common terminal 1007 toward the low-pass filter 1002 of the transmitting side, is ideally adjusted to be in an open state, the received signal is not transmitted to the transmitting terminal 1005.
However, when the above described constitution is used in the case where a system using the frequency division system which is a simultaneous transmission and reception coexists with a system which is a non-simultaneous transmission and reception, there arose a problem that a loss becomes larger than when the antenna switch was used.